Toán Lớp 6: Bài 6. Tìm số nguyên x,y sao cho:
a) (2x +1). (3-y) = 5
b) xy + x + y =4
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Toán Lớp 6: Bài 6. Tìm số nguyên x,y sao cho:
a) (2x +1). (3-y) = 5
b) xy + x + y =4
Comments ( 1 )
a) (2x+1).(3-y) = 5
= 5.1 = (-5).(-1)
Nếu (2x+1) = 5 thì (3-y)= 1
⇒ x = 2; y = 2
Nếu (2x+1)= 1 thì (3-y)=5
⇒ x = 0; y = -2
Nếu (2x+1)= -5 thì (3-y) = -1
⇒ x = -3; y = 4
Nếu (2x+1)= -1 thì (3-y)= -5
⇒ x = -1;y = 8
Vậy x={2;0;-3;-1}
y={-2;2;4;8}
b) xy + x + y = 4
⇒x(y+1) + y = 4
⇒x(y+1) + y +1 -1 = 4
⇒(y+1)(x+1) = 5
Mà 5 = 5.1 = (-5).(-1)
Nếu (y+1)= 5 thì (x+1)= 1
⇒ y = 4;x = 0
Nếu (y+1)= 1 thì (x+1)= 5
⇒y = 0; x = 4
Nếu (y+1)= -5 thì (x+1)= -1
⇒y = -6;x = -2
Nếu (y+1)= -1 thì (x+1)= -5
⇒y = -2; x = -6
Vậy x = {0;4;-2;-6}
y = {0;4;-2;-6}